To meet the demand for wireless data traffic, which has increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’.
It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like.
In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple Access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed.
Mobile communication systems have rapidly evolved, and recently have evolved to reflect user's various demands to support high-speed large-capacity services. Service providers are deploying small cells as well as macro cells in order to support high-speed large-capacity services for a user. The small cell is deployed to use a frequency which is higher than a frequency of the macro cell thereby supporting a data transmit rate which is higher than a data transmit rate of the macro cell. If it is difficult for the macro cell to support a new service which is provided in the mobile communication system, the mobile communication system may support the new service using the small cell which supports the relatively high data transmit rate.
Generally, even though a macro cell is deployed with a small cell in the mobile communication system, a user equipment (UE) may receive a service through only one of the macro cell and the small cell. However, in an evolved mobile communication system, the UE may receive a service through the both the macro cell and the small cell using a dual connectivity scheme.
A structure of a mobile communication system where a macro cell and a small cell are co-located is described below with reference to FIG. 1.
FIG. 1 schematically illustrates a structure of a mobile communication system where a macro cell and a small cell are co-located according to the related art.
Referring to FIG. 1, the mobile communication system includes a mobility management entity (MME) 111, a serving-gateway (S-GW) 113, a packet-gateway (P-GW) 115, a macro enhanced node B (eNB) 117, a plurality of small cell eNBs (e.g., eight small cell eNBs) 119-1, 119-2, 119-3, 119-4, 121-1, 121-2, 121-3, and 121-4, and a UE 123. The small cell eNBs 119-1, 119-2, 119-3, and 119-4 are included in a small cell cluster 119.
The UE 123 is connected to each of the macro eNB 117 and the small cell eNB 121-2, the macro eNB 117 is connected to each of the MME 111 and the S-GW 113, and the small cell eNB 121-2 is connected to the S-GW 113. Alternatively, the small cell eNB 121-2 may not be connected to the S-GW 113; in this case, the small cell eNB 121-2 is connected to the macro eNB 117. The UE 123 may be connected to the macro eNB 117, the small cell eNB 121-2, or the macro eNB 117 and the small cell eNB 121-2. The UE 123 may have a dual connection with the macro eNB 117 and the small cell eNB 121-2.
As described above, the UE 123 establishes a connection with each of the macro eNB 117 and the small cell eNB 121-2 at the same time (i.e., the UE 123 establishes a dual connection) thereby transmitting/receiving data with the macro eNB 117 and the small cell eNB 121-2. However, if the UE 123 is a hardware device which has a difficulty in establishing a connection with each of the macro eNB 117 and the small cell eNB 121-2 at the same time, or there is a difference between a transmit power which is used in the macro eNB 117 and a transmit power which is used in the small cell eNB 121-2, the UE 123 may be restricted on receiving a service through a dual connection from the macro eNB 117 and the small cell eNB 121-2.
In the mobile communication system, in a case that the macro eNB 117 is deployed to use a relatively low frequency band, and the small cell eNB 121-1 is deployed to use a relatively high frequency band which is not adjacent to a frequency band of the macro eNB 117, an implementation form of the UE 123 that the UE 123 establishes a connection with the macro eNB 117 and the small cell eNB 121-1 at the same time to transmit/receive data to/from the macro eNB 117 and the small cell eNB 121-1 is easier than an implementation form of the UE 123 that only the small cell eNB 121-1 supports relatively high data transmit rate for the UE 123 in terms of implementation.
Accordingly, in a mobile communication system, a UE may be connected to both a macro eNB and a small cell eNB to receive a service from both the macro eNB and the small cell eNB by separating a timing point at which the UE is connected to a macro eNB and a timing point at which the UE is connected to a small cell eNB (i.e., by using a time division multiplexing (TDM) dual connectivity scheme). There is a need for a scheme that a UE effectively performs a switching operation between a macro eNB and a small cell eNB. There is a need for a scheme of performing a switching operation in order to effectively provide a service to a UE in a case that the UE is connected to different types of cells using a dual connectivity scheme.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.